1200A Ground Fault Setting on Main

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philly

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How do others typically approach the ground fault setting for a facility main breaker when there is no ground fault on the feeders or any downstream devices?

I'm looking at a 1200A Service Entrance SWBD with GF on 1200A main but no other levels of ground fault. I know per 230.95 it allows a maximum setting of 1200A.

In the past I have seen the approach of always setting main breaker to 1200A with time delay and then coordinating everything downstream. I'm curious to hear from others how they typically approach this setting when setting it at something other than the 1200A max?
 
I have found the time delay is usually more important than the pickup amps.

I have also found that it is all but impossible to coordinate with branch breakers larger than 70A unless two levels of GF are provided.

The end result is a potential for unintended GF tripping exists unless coordination was considered at the design stage.
 
I'd set it at 1/2 to 2/3 pickup with a 0.3 to 0.4 second delay, depending on the size of the phase-trip devices. That should give phase devices enough time to be selective for phase-to-ground faults.
 
If all the settings are at minimum, I will bump them up one notch if need be, but if the nuisance tripping continues, I defer the customer to get an engineered coordination study, and let it fall back on the engineers! LOL!
 
The time delay is the key setting. The faster it trips, the more it will mis-coordinate with downstream molded case breakers. As Jim said, usually 70 A to 100 A is about the largest breaker that will coordinate. The ground fault protection requirement was driven by fire prevention, not shock hazard or coordination. I usually have them set at maximum delay.
 
Set the main GF to maximum allowable per code. When you do this you’ll see many LSIG breakers in that frame size are not capable of this setting giving the coordination problems you mention. You’re better off with an LSI breaker and a GF relay to shunt trip the said main so you have flexibility in setting to the max to achieve coordination. Coordination and arc flash/gf protection is always a balance. Give the engineer doing the power study the ability to attempt to satisfy both criteria to the degree practicable.
 
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